What is hash function ?!
Hash function maps a variable length message into a fixed length hash value.
Cryptographic hash function is an algorithm for which no attack is more efficient than brute force to find
1- Get the message from the hash value.
2- Find two messages with the same hash value.
Building a simple hash function The simplest form of hash function is bit-by-bit XOR but it is not secure at all h = B1 ⊕ B2 ⊕ B3 ….
